1. Field of the Invention
The present invention relates to an apparatus that monitors the state of a battery based power supply, which provides an operating power for electric appliances installed in a vehicle.
2. Description of the Related Art
In recent times, electric appliances (electric devices), such as televisions, food heating/chilling units and vacuum cleaners, have tended more and more to be included as installed equipment in vehicles. To operate such electric appliances in a vehicle, power is generally supplied via a cigarette lighter socket, or via a plurality of specially provided power supply outlets (accessory outlets), and as a result, to operate such electric devices there has been a corresponding increase in the battery supplied power that is required. Under the circumstances, to protect batteries in vehicles and to prevent them from being damaged, monitoring apparatuses have had to be employed for controlling, an halting when necessary, the supply of power to electric, vehicular appliances.
A conventional example is a vehicle power supply monitoring apparatus disclosed in Japanese Patent Unexamined Publication No. Hei. 5-208645. This monitoring apparatus comprises: a current monitoring circuit, for halting the supply of power along a power feeding path leading to a power supply outlet when the current flowing through the power supply outlet exceeds a setup value; and a voltage monitoring circuit, for halting the supply of power along the power feeding path to the power supply outlet when the output voltage at a battery has been reduced and is less than or equals a lower setup voltage limit. The current monitoring circuit and the voltage monitoring circuit protect the battery from overcurrents and from reductions in the output voltage.
The conventional monitoring apparatus halts the supply of power when an overcurrent is detected and a current value exceeds a predetermined setup value.
Actually, the loads connected to power supply outlets in a vehicle comprise a variety of electric appliances, such as lamps and motors. Therefore, although for a short period of time a current, such as a lash current or a motor-lock current, at a power supply outlet may frequently equal or exceed a rated current, since the time span for a lash current or for a motor-lock current is very brief, the load imposed on a battery is small and the current flowing along a power feeding path need not be interrupted.
Therefore, in order that a large current, such as a lash current that flows for a brief period of time, is not detected, for the conventional monitoring apparatus a setup value must be set that equals or exceeds a lash current value. As a result, the setup value becomes too large and a battery can not be effectively protected from an overcurrent, and the consumption, due to an overcurrent, of the power stored in a battery that is less than or that equals the setup value can not be prevented.
Further, the conventional monitoring apparatus is so designed that it does not interrupt a current flowing along a power feeding path until the output voltage of the battery providing the current has been reduced and equals or is less than the lower voltage limit, or unless a current equaling or exceeding a setup value has flowed to an electric appliance. Therefore, when the amount of current that is supplied is increased within a range that is smaller than the setup value, a reduction in the voltage output by the battery can not be prevented.
To resolve the above problem, it is a first object of the invention to provide a power supply monitoring apparatus for vehicle that can effectively protect a battery from overcurrents, and that can prevent, within a required range for battery protection, placing limits on the employment of electric appliances.
It is a second object of the invention to provide a power supply monitoring apparatus for vehicle that can prevent the excessive consumption of the power stored in a battery by an increase in the currents that are supplied.
In order to achieve the above objects, according to the invention, there is provided a power supply monitoring apparatus for vehicle, which monitors the state of a power supplied by a battery to an electric appliance, comprising: a cutoff unit, which is located along a power feeding path between the battery and the electric appliance, for interrupting a current flowing along the power feeding path; a current detector for detecting the value of a current flowing across the electric appliance; and a first command unit, for which a plurality of different reference current values and a plurality of corresponding permitted times are set, for detecting a condition wherein the value of the current detected by the current detector equals or exceeds at least one of the plurality of the reference current values, is continued for a period that equals or exceeds one of the plurality of the permitted times that corresponds to the reference current value, and for outputting a command to the cutoff unit to interrupt the current flowing along the power feeding path.